The present invention relates to methods and systems for calculating a blocking probability associated with a network.
In recent years, the demand for wireless voice and data services has increased dramatically. In order to keep up with these demands, wireless network providers have focused on methods to increase the capacity of their existing wireless networks. Various methods have been employed to avoid users being denied access to the network either during call initiation or roaming.
For example, mobile communications is typically implemented using a cellular radio network as shown, for example, in FIG. 1. As shown, a cellular network 100 is divided into a plurality of cells 124. Each cell defines an individual radio coverage area, i.e., a geographic area, served by a radio base station 126. In a GSM cellular network, individual calls within a single cell use different combinations of frequencies and slots. The frequencies may be reused by other cells provided there is no interference with other cells. The frequency reuse pattern of the cells is dependent on the distance between the cells and the radio transmission power.
In modern cellular networks, a cell may, in fact, consist of one or more “sectors”; the term sector is used to mean a geographic area within a cell that is served primarily by a specific set of frequencies, as well as that set of frequencies. Hereafter, we use the word “cell’ interchangeably with the word “sector” to denote a sector.
Each base station 126 is connected to a centralized switch or mobile switching center 128 that provides switching capabilities and acts as a gateway to wired networks such as the public switched telephone network (PSTN), the Internet, and other public and private data communications networks. On the customer side, users connect to the wireless network through wireless mobile nodes or stations 130 that can act as transmitters and receivers. The mobile nodes 130 communicate with the base stations 126 over wireless communications links 138.
In general, the number of calls that a network can handle is based upon the number of channels in the network. With respect to a GSM wireless network, the number of channels depends, in part, on the number of frequencies supported by the base stations. Calls placed when the network's channels are busy are not completed, i.e., are blocked.
As a mobile station 130 moves about in the network 100, it may need to switch between base stations 126 in different cells. Handoff encompasses a process supported between a mobile station and the network that allows the mobile station to move from one cell to another while a call is in progress. If handoff cannot be completed, then the call will likely be dropped or terminated.
If a call is blocked by one base station, then the call may be redirected to one or more alternative base stations that are also accessible to the mobile station This applies both to originating and hand-off calls. This is generally referred to as a directed retry. The purpose of directed retry is to increase the effective capacity of a network by making it possible for calls to be served by multiple base stations (so long as the frequency assignments reduce co-channel interference and provide calls with low-interference access).
The likelihood that the network will not be able to complete a call, i.e., the network blocking probability, is related to the number of calls received by the network, the number of channels in the network, and the routing scheme (the set of redirection sequences) used by the network. Given the network configuration and a routing scheme, a network provider tries to reduce the blocking probability so that fewer calls are dropped.
Of utility then are methods and systems for calculating and predicting call blocking in a network.